Failure analysis of RC structures retrofitted with nano-enhanced FRP systems

A prominent priority of the research community regards the investigation of the applicability of nanotechnology in the construction industry, in order to obtain high-performance building structures. To this end, in the present work, a numerical study on the failure behavior of reinforced concrete (RC)structures retrofitted with nano-enhanced FRP systems has been developed by using a cohesive zone model. The adopted model relies on an inter-element fracture approach to simulate the cracking and debonding phenomena occurring in the concrete phase and strengthening system, respectively. In particular, cohesive elements, equipped with suitable traction-separation law, are inserted between all adjacent bulk elements of the concrete, able to describe the nonlinear fracture processes such as multiple crack onset and propagation. On the other hand, a new cohesive bond-slip model is proposed to simulate the debonding phenomena of the FRP reinforcement, able to take into account the reinforcing effect induced by theincorporation of nanomaterials into the epoxy adhesive. The proposed numerical strategy is first validated by performing a shear test of concrete prisms reinforced with FRP sheets and then employed to simulate the mechanical behavior, including the failure stage, of RC beams strengthened with a nano-enhanced FRP plate. The comparisons with experimental outcomes show the reliability and effectiveness of the proposed model to predict the structural response of such kinds of structures, in terms of loading curve and crack patterns, emphasizing the beneficial effects of the nano-enhanced epoxy on bond strength between concrete and FRP systems.